I've recently discovered when using calcualted data expressions, such as WORKMINUTESDIFF, in text mode reporting or in calculated fields, the calculation references the instance's default schedule rather than the schedule associated with the project you're reporting on (or the project that the task/issue you're report on is in).
This formula in a calculated field was using the default schedule
WORKMINUTESDIFF(Project.Converted Issue Entry Date,Actual Completion Date)
In order to account for the time zone and holidays of a project for one of our EU teams, I have to include the schedule ID as part of the formula in this way:
WORKMINUTESDIFF(Project.Converted Issue Entry Date,Actual Completion Date,"61858bd400325ef77ff7f86977d0b5ae")